Virago XV1000 Carburetor Tuning.

Paul Sutton

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Thanks 5twins. I will enjoy the learning part, but not the carb removal. The Hitachi does not have clip slots, you just stack the washers on and a spring holds it all in place. I ordered some more BP7ES plugs so I have clean porcelain to start with. Next rainy days are a week away.
 

Paul Sutton

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Made a 0.5mm brass washer on the lathe. Reassembled everything and tested the engine in the garage. I thought I heard a faint hiss so tightened the carb boots up further. The hiss stopped but the engine would stall when I sprayed carb cleaner on the boot. Carbs out and close inspection shows a crack in the boot...:doh:

But look at the bright side, I've probably found the root cause...:hump:...testing to resume in a week's time with new boots.
 

Paul Sutton

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Here we are 9 Days later. I have receive the carb boots and fitted them. There are no signs of any air leaks now. With new plugs fitted and both pilot screws set quite high I have made some tests:
1. Rode at 50 - 60 mph for 9 miles on a long straight motorway grade road then killed the engine and cruised to a stop. Both plugs were white but with no sign of blistering to the insulator.
2. Riding around town then resulted in the rear plug staying white but the front started going brown. The exhaust is also smelly at idle.

The front plug fouling around town is easily solved with the pilot screw so this I will do first. Then I will fit a 0.5mm washer to each carb needle and see what this does at 50 - 60 mph.

So how does that sound?


Side Issue: Virago XV1000 Hitachi Carb pistons:
Needle assembly has a plastic cap that screws down over the spring to hold it in place.
Carb 3.JPG

A view from below the piston with the needle removed. At the 9 o'clock position is a brass pin.
Carb1.JPG

A view from the diaphragm end zooming in on the base where the needle sits.
Carb2a.JPG
The brass pin rises above the surface preventing the needle assembly sitting flush with the surface. What is the purpose of this???

Thank you for any comments.
 

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Rented Mule

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Hi Paul, I’m late to the conversation and way behind on your current situation. However, I do have a couple suggestions (my opinions are always free of charge) First, mark your throttle hand grip into quadrants, i.e. 1/4, 1/2, 3/4, and full. By doing so you can tell exactly which carburetor circuit is at fault. Google, motorcycle carburetor theory 101, it’s an old article but does a good job of explaining the various carburetor circuits by throttle position (https://nanopdf.com/download/file-6783_pdf.)
Second option, if you can find an auto shop that has a exhaust gas analyzer you can get a good idea of what the carbs are doing individually and differences between the two units.
Third option, though not very practical as this is usually directed toward piston driven aircraft, is monitoring the exhaust gas temperature. Aircraft EGT analyzers take direct exhaust temperatures and displays the various cylinder temperatures caused by the fuel/air mixture ratios due to altitude and throttle position.
Bonus option, make daily Jack Daniels sacrifices to the great Hitachi Gods as I have found this is the only way to truly understand these carburetors.
E6823C5D-AE27-45DB-9B1E-B52AB09CB409.jpeg
Here’s my Hitachi HSC40 headache.
8620D980-C4F6-43CA-AEA1-30F9AC70AE04.jpeg
 
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5twins

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Unfortunately, the throttle position thing doesn't work so well with CV carbs because the slide isn't directly connected to the throttle cable. For instance, half throttle doesn't necessarily mean the slide is half open. These CV carbs lift their slides by engine demand. So for tuning purposes, you're better off noting the RPM that the issue occurs at rather than throttle opening amount.
 

Paul Sutton

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Thank you for all the comments. I am considering the CO analyser route and I intend marking my throttle just to confirm my feeling that most of my riding is at the low end. I have been attempting to sync my carbs today but gave up due to the inaccessibility of the adjustment screw. I then spent an hour or two making a special socket to connect with the adjuster screw and to also fit my 1/4" flexible extension. It seems to work well so I've tucked it in bed for the night. I still have another 0.5mm brass washer to part off on the lathe this comming week.

Tomorrow I shall have better luck...:umm:
 

Rented Mule

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Unfortunately, the throttle position thing doesn't work so well with CV carbs because the slide isn't directly connected to the throttle cable. For instance, half throttle doesn't necessarily mean the slide is half open. These CV carbs lift their slides by engine demand. So for tuning purposes, you're better off noting the RPM that the issue occurs at rather than throttle opening amount.

I think generally we are saying the same thing - throttle position equals RPM. What I’m trying to say is by noting your throttle position this will give you a better idea of which fuel circuit is controlling and a place to start troubleshooting.
upload_2021-7-11_0-3-39.jpeg


This video does a lot better job explaining how a CV carburetor works -
 
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Paul Sutton

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Thank you Rented Mule. I managed to get the carbs sync'd and added the 0.55mm washers I made up on the lathe. The bike is reassembled but the rain has arrived so I'll have to wait for fine weather later in the week. The throttle will get its markings in Tipex tonight. I added the 0.55 mm washers because I know there is a lean issue in that part of the circuit from my recent ride, not excessively lean but worth a learning experiment to better understand carburetors.
 

Rented Mule

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Congratulations on getting your carbs sync’d. Now I have to focus my attention on finding the engineer who designed the Hitachi HSC40 carburetors. I have a few choice words I would like to convey to that person.
 

Paul Sutton

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Have you struck an issue with the HSC40s? I may have seen the topic covered on a Virago website.
 

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Just been on a 50 - 60mph sprint up the road for approx 9 miles then cut the engine and cruised to a stop. With the 0.55mm washers fitted to both carburetors I have good news:

Front Cylinder: This was fine previously but the 0.55mm washer has now made it rich to the extent that only the top 1mm of the plug insulator is self-cleaning. So out that washer comes, but an interesting experiment as I did not expect such a big change to occur.

Rear Cylinder: This was running lean previously. With the 0.55mm washer inserted it looks good. The ground electrode/strap has obviously cooled off some and the insulator is self-cleaning nicely. So this carburetor will keep its washer.

Thank you everyone for the comments, I feel happier :cheers:.
 

Paul Sutton

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Here is a view of the plugs with the yellow arrow showing the position of the heat line that the ground electrode/strap is cleaning to. Previously the cleaning line was all the way back to the weld joint on the lean rear cylinder.

Front Cylinder Plug:
FrontPlug.JPG

Rear Cylinder Plug:
RearPlug.JPG
 

5twins

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When "reading" plugs, besides looking at the ground strap, you also want to look at the porcelain around the center electrode. It should have a ring of color around the bottom called the "smoke" or "mixture" ring .....

oh9jQbN.jpg


I don't like to see it rising much more than a quarter of the way up. In your 1st pic of the front cylinder plug, the porcelain is nearly completely covered. That would indicate to me it's running a bit rich. Unless that pic was taken right after a cold start using the choke. That will blacken the porcelain up and it takes a good ride to burn it clean again.
 

Paul Sutton

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Thank you 5twins.

The plugs are as they appeared after cutting the engine at 50 - 60mph. Hence my conclusion to remove the washer. from the front carb. Back in Entry #11 I show the plug for the lean rear cylinder after chopping it in the lathe. I assume it will now have a darker ring with the 0.55mm washer inserted, certainly the ground electrode is running slightly cooler.

I will run the bike later this week once the front carb washer has been removed and will chop the rear plug in the lathe to get a view of 50 - 60mph performance.
 

5twins

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I never went that radical, actually cutting a plug open, lol. I just look down into them as best I can with a little flashlight. It's pretty easy to see the "smoke" ring if it gets too high, like in your one pic.

One time I was experimenting on my '78. After all, that's what carb fine tuning is all about really, experimenting, lol. The plugs looked good with a "smoke" ring down near the bottom of the porcelain, but I wanted to see just what difference moving the needles a step richer would have. Would the bike run better? Would it perform better? Would the plugs turn black as a moonless night, lol? Well, it didn't seem to affect running or performance much, and it didn't turn the plugs all black, but the smoke ring did climb up so it was now covering 2/3 to 3/4 of the porcelain. Definitely too rich. Needle position has a big effect on plug color because it's tuning the midrange and that's where you spend most of your time running.
 

Paul Sutton

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The final comments:
  1. Both boots cracked and leaking, so replaced.
  2. Rear Pilot screw missing Oring and jet blocked, all sorted.
  3. 0.55mm washer added to rear lean carb, now running nice.
  4. Carbs synchronised and Pilot screws reset to same values.
After 160 mile ride the plugs were both clean and off white slightly. When tested with a Gunson Colortune plug both cylinders are showing blue and the pilots have been adjusted slightly to eliminate exhaust popping on deceleration: Front Pilot = 2.00 Rear Pilot = 1.75

I'm happy, the Bike's happy so thanks for all the ideas and I consider this closed.
 

Jan_P

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My best friend died last summer and his daughter shall now sell a Virago that has been parked many years
ca 10 years
In cold storage

A Yamaha 1100 Virago 1991 Black paint
58000 Km --36000 miles
Last time I saw it it was in fine condition

Is it a big mistake trying to start it without cleaning out carburetors ??
Is it a sought after bike . anything else.one should know ?
It is early days in the sales Process -- I am not fully informed of status but has been asked for advice But as it seems no serous offer ..As I would expect this time of year.. I have recommended to wait a while.
What would be a reasonable price according to you gentlemen
 

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Paul Sutton

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Regarding the Carburetors, it is a real effort to work on the Virago. In 91 they were fitted with Mikuni carbs whereas my 88 XV1000 has the old Hitachi carburetors. The following YouTube shows how much effort is required:


You can try starting the Virago without cleaning the carbs, but if it were stored with petrol in the tank/carburetors there might be blocked jets. I would put about 5 - 10ml of 2-Stroke oil in each cylinder and turn the engine over with the plugs out just to oil the cylinder walls before attempting a start. Turning the engine over with the plugs out will prime the oil pump and get some oil up to the cam bearings and rockers.

2-Stroke oil will burn off very quickly and cleanly.
 

Jan_P

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Thank you Sir
If anybody is interested
the first offer was 5 -700 Euro
Now it is up to 1000 Euro
I have told ( Recommended ) her Not to sell at that price Even though it can be a price in winter for a non starter.
I have not seen the bike for a while ---But I assume at least 1700 euro for a starter in 3 -4 months time.
Feel free to comment
 
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